Childhood depression was almost unthinkable until several years ago. Now we not only know that major depressive disorder (MDD) exists in children and adolescents, but that it is also a common condition. Early-life MDD has been correlated with antisocial personality, bipolar disorder, and suicide. It is estimated that youngsters who suffer from depression often develop conduct and anxiety disorders, and that 20-25% develop substance abuse disorder. Consequently, this has resulted in a disproportionate increase in the prevalence of, antidepressants prescribed to youths below 20 years of age. Despite the heightened rates in antidepressant use, little is known about the long-term behavioral and neural adaptations resulting from antidepressant treatment during periods before adulthood. To address this need in our basic knowledge, the experiments described in this proposal will examine the behavioral responses to antidepressant treatment in "adolescent" rats (postnatal day [PD] 35), and will further assess the long-term behavioral consequences of adolescent antidepressant treatment in adulthood (PD90+). This will be accomplished within the framework of the following specific aims: [1] determine the efficacy of antidepressant treatment in juvenile rats, [2] assess long-term consequences of chronic adolescent antidepressant treatment on the sensitivity to reward- (natural, drug) and mood-related (anxiety, stress) behaviors in adulthood, and [3] evaluate the integrity of reward-related biological markers [extracellular signal regulated protein kinase (ERK)], within the mesolimbic system, following chronic adolescent antidepressant exposure. We expect that antidepressant exposure during adolescence will induce long-lived alterations associated with responses to stress, anxiety, natural- and drug-rewarded behaviors. Furthermore, we expect site-specific neurochemical alterations (ERK fluctuations within the ventral tegmental area) to be a factor mediating these mood- and reward-related alterations as a function of early-life antidepressant exposure.